Phylogenetic trees are a central tool for studying language evolution and have wide implications for understanding cultural evolution as a whole. For example, they have been the basis of studies on the evolution of musical instruments, religious beliefs and political complexity. Bayesian phylogenetic methods are transparent regarding the data and assumptions underlying the inference. One of these assumptions—that languages change independently—is incompatible with the reality of language evolution, particularly with language contact. When speakers interact, languages frequently borrow linguistic traits from each other. Phylogenetic methods ignore this issue, which can lead to errors in the reconstruction. More importantly, they neglect the rich history of language contact. A principled way of integrating language contact in phylogenetic methods is sorely missing. We present contacTrees, a Bayesian phylogenetic model with horizontal transfer for language evolution. The model efficiently infers the phylogenetic tree of a language family and contact events between its clades. The implementation is available as a package for the phylogenetics software BEAST 2. We apply contacTrees in a simulation study and a case study on a subset of well-documented Indo-European languages. The simulation study demonstrates that contacTrees correctly reconstructs the history of a simulated language family, including simulated contact events. Moreover, it shows that ignoring contact can lead to systematic errors in the estimated tree height, rate of change and tree topology, which can be avoided with contacTrees. The case study confirms that contacTrees reconstructs known contact events in the history of Indo-European and finds known loanwords, demonstrating its practical potential. The model has a higher statistical fit to the data than a conventional phylogenetic reconstruction, and the reconstructed tree height is significantly closer to well-attested estimates. Our method closes a long-standing gap between the theoretical and empirical models of cultural evolution. The implications are especially relevant for less documented language families, where our knowledge of past contacts and linguistic borrowings is limited. Since linguistic phylogenies have become the backbone of many studies of cultural evolution, the addition of this integral piece of the puzzle is crucial in the endeavour to understand the history of human culture.

系统发育树是研究语言进化的核心工具，对理解整个文化进化具有广泛的意义。例如，它们一直是研究乐器演变、宗教信仰和政治复杂性的基础。贝叶斯系统发育方法对于推断所依据的数据和假设是透明的。这些假设之一——语言独立变化——与语言进化的现实不相容，尤其是语言接触。当说话者互动时，语言经常相互借用语言特征。系统发育方法忽略了这个问题，这可能导致重建错误。更重要的是，他们忽视了丰富的语言接触历史。一种在系统发育方法中整合语言接触的原则性方法非常缺失。我们提出contacTrees，一种用于语言进化的具有水平迁移的贝叶斯系统发育模型。该模型有效地推断出语言家族的系统发育树及其进化枝之间的联系事件。该实施可作为系统发育软件 BEAST 2 的一个包提供。我们在模拟研究和案例研究中应用了contacTrees，该研究对记录良好的印欧语言的子集进行了研究。模拟研究表明，接触树正确地重建了模拟语言家族的历史，包括模拟的接触事件。此外，它表明忽略接触会导致估计的树高、变化率和树拓扑的系统误差，这可以通过接触树来避免. 案例研究证实了contacTrees重建印欧语历史上已知的接触事件并找到已知的借词，展示其实际潜力。与传统的系统发育重建相比，该模型对数据的统计拟合度更高，重建的树高明显更接近经过充分证明的估计。我们的方法弥补了文化进化的理论模型和经验模型之间长期存在的差距。这些影响对于记录较少的语言家族尤其重要，因为我们对过去的接触和语言借用的了解是有限的。由于语言系统发育已成为许多文化进化研究的支柱，因此添加这个完整的拼图对于理解人类文化历史至关重要。